Guess what? This was misreported, but it doesn't seem like anyone (myself included) properly fact-checked.

Thanks to an eagle-eyed catch by Ryan Gallagher at CriterionCast, we now know this is not true. Timm is temporarily stepping away from those duties, which are being handed off to James Tucker for the time being, to pursue "other projects set up at Warner Bros". WB PR rep Gary Miereneau goes further to say that Bruce Timm "will be back" to do more there.

I wonder if WB is doing the smart thing and pulling him into something approximating what Joss Whedon is doing for Marvel...one could hope...